The objective of this proposal is to provide increased understanding, at the molecular level, of the mechanisms of activation of intrinsic blood coagulation, kinin generation and fibrinolysis. Factor XII activation induced by negatively charged substances, as well as interactions among factors XII and XI, prekallikrein, high molecular weight kininogen and plasminogen, will be investigated. These studies will utilize fluorescence polarization, fluorescence resonance energy transfer, enzyme kinetics, and rapid reaction stopped-flow kinetic techniques. Quantitative data will be obtained for the stoichiometries, affinities and rates of the various interactions involved, using purified systems as well as normal and factor-deficient plasmas. It is anticipated that successful completion of this project will result in enhanced understanding of the molecular mechanisms of contact activation, as well as the relative importance of each factor XII-dependent pathway.